This invention relates to a method of manufacturing a color filter and, more particularly to a method of manufacturing a color filter for use in liquid crystal display devices.
The use of color displays in liquid crystal display devices is known in the art. Color liquid crystal displays are being used more frequently as computer terminals in view of the rapid advance of liquid crystal technology in recent years. The liquid crystal display devices include two substrates with liquid crystal material disposed therebetween. The inner surface of each substrate has a plurality of parallel ribbon-like electrodes, with the electrode ribbons on one substrate arranged perpendicularly to the electrode ribbons on the other. The areas in the device where the electrodes on one substrate intersect the electrodes of the other substrate are known as pixels.
Within this model, liquid crystal display devices, colorized or not, are usually classified as either utilizing an active matrix system or a simple matrix system. The active matrix system necessitates an active element, such as a thin film transistor (TFT) or diode, at every pixel in the display. The simple matrix system requires only a drive circuit connected to each ribbon-like electrode. The simple matrix system takes advantage of the steep threshold characteristics of certain liquid crystal materials.
Ferroelectric liquid crystal material has such a steep threshold characteristic. It is contemplated that these compounds will be used in liquid crystal display devices employing the simple matrix system. Presently in use is the double-layer super-twisted nematic (STN) system and the film compensating STN system.
In the simple matrix or any display system requiring a steep threshold characteristic, the substrate and any color filters positioned on the substrate must be substantially flat to keep the threshold characteristic uniformly steep over the entire area of the display. If uniformity is not maintained, the picture quality becomes less than completely satisfactory. Thus, it is indispensable that any process for forming the color filter for use in a simple matrix system display device must have a precise flat color filter surface.
Various methods of forming color filters are presently known in the art. These methods include printing, dyeing, and electrodeposition methods. Another method which has been developed within recent years is the color photoresist method. In this method, pigments are dispersed in a negative resist material and formed into patterns by photoresistance. This method is superior to the printing method in positional precision and the flatness of the color filter surface. The method also has better heat resistance and light stability than the dyeing method. Additionally, the photoresist method allows for a greater variety of patterns and is less expensive to manufacture than the electrodeposition process. Recently, problems associated with the photoresist method, including the hue quality and liquid stability, have been solved, thereby increasing the popularity of the photoresist method of forming color filters.
Current methods of forming color filters are less than completely satisfactory. They are still moderately expensive, and the resulting surface of the color filters still is uneven. This leads to variances in the threshold characteristics and less than completely satisfactory picture quality in simple matrix system display devices.
One such photoresist method of forming color filters in shown in FIG. 1. Color resists of different hues are superposed on each interpixel clearances. A plurality of a first formed pixels 102 are formed on a transparent substrate 101. A plurality of a second formed pixels 103 of a color different from first formed pixels 102 are formed on transparent substrate 101 with a plurality of superposed portions 105 overlapping onto first formed pixels 102. A plurality of a third formed pixels 104, different in color from both first formed pixels 102 and second formed pixels 103, are formed on transparent substrate 101 with a plurality of superposed portions 106 and 107 on second formed pixels 103 and first formed pixels 102, respectively. The presence of superposed portions 105, 106 and 107 cause the surface of the color filters to be uneven. In order to achieve a flat surface, another film must be provided on the filters and ground to a flat surface, at additional expense.
Another known photoresist method of forming color filters is shown in FIG. 2. To avoid the overlapping of the prior example, a plurality of black thin shading layers 201 are formed on transparent substrate 101 before the forming of pixels 102, 103 and 104. The surface of the pixels formed are thus flat. However, this method is expensive since thin shading layers 201 are formed by coating the material on substrate 101 by vaporization and patterning by photoetching. Additionally, this method results in interpixel gaps 202 between the color filters, and so, like in the previous method, the film next positioned on the filters will tend to be uneven.
Accordingly, it is desirable to provide a photoresist color filter manufacturing method which overcomes the disadvantages of prior art photoresist methods and is inexpensive and provides a relatively flat color filter surface layer.